1. Technical Field
The present disclosure relates to a method of manufacturing a substrate that includes a through hole formed in a silicon substrate and a through electrode formed in the through hole and being insulated form the silicon substrate.
2. Related Art
In the past, a substrate (see FIG. 1), which includes a through hole formed in a silicon substrate and a through electrode formed in the through hole and being insulated form the silicon substrate, has been used as a substrate (interposer) that electrically connects a semiconductor device with a mounting substrate such as a mother board.
FIG. 1 is a cross-sectional view of a substrate in the related art.
Referring to FIG. 1, a related-art substrate 200 includes a silicon substrate 211, an insulating film 212, a through electrode 213, and wiring 214. The silicon substrate 211 has a plate shape, and includes a through hole 216. The through hole 216 is formed so as to pass through the silicon substrate 211 by a Bosch process. The Bosch process is a deep etching technique for silicon, specifically, an etching method of repeatedly performing etching (etching step) and etched sidewall protection (protecting step). Isotropic etching is performed using sulfur hexafluoride (SF6) in the etching step, and a sidewall is protected (etching performed in a transverse direction is controlled) using Teflon (registered trademark) gas (for example, C4F8) in the protecting step. Since the etching step and the protecting step are repeatedly performed in the Bosch process, the side surface of the through hole 216 formed by the Bosch process has a scalloping shape (where fine unevenness is repeatedly formed). The thickness of the silicon substrate 211 may be, for example, 200 μm.
The insulating film 212 is formed to cover both surfaces 211A and 211B of the silicon substrate 211 and the surface of a portion of the silicon substrate corresponding to the side surface of the through hole 216. The insulating film 212 is a film that insulates the silicon substrate 211 from the through electrode 213 and the wiring 214. For example, an oxide film may be used as the insulating film 212.
The through electrode 213 is formed in the through hole 216 on which the insulating film 212 is formed. The upper end of the through electrode 213 is a portion on which a semiconductor device 201 is mounted, and the lower end of the through electrode 213 is connected to the wiring 214.
The wiring 214 is formed on the lower surface of the insulating film 212, which is formed on the lower surface 211B of the silicon substrate 211. The wiring 214 is connected to the lower end of the through electrode 213. The wiring 214 includes a pad portion 218 on which an external connection terminal 203 is provided. The pad portion 218 is electrically connected to a pad 205, which is provided on a mounting substrate 202 such as a mother board, through the external connection terminal 203.
FIGS. 2 to 7 are views illustrating steps of manufacturing the substrate in the related art. In FIGS. 2 to 7, the same components as those of the substrate 200 in the related art are represented by the same reference numerals.
A method of manufacturing the substrate 200 in the related art will be described with reference to FIGS. 2 to 7. Firstly, in a step illustrated in FIG. 2, a protective tape 221 is attached to the lower surface 211B of the silicon substrate 211 and a resist film 222 having an opening 222A is then formed on the upper surface 211A of the silicon substrate 211. The protective tape 221 is a tape for preventing a stage of an etching apparatus (not shown) from being etched when the silicon substrate 211 is etched by the Bosch process. The opening 222A is formed so that the portion of the upper surface 211A of the silicon substrate 211 corresponding to a forming region of the through hole 216 is exposed to the outside. Meanwhile, the thickness of the silicon substrate 211 in this step is larger than that of the silicon substrate 211 shown in FIG. 1. Specifically, the thickness of the silicon substrate 211 shown in FIG. 2 may be, for example, 250 μm.
In a step illustrated in FIG. 3, the silicon substrate 211 is etched by the Bosch process that uses the resist film 222 as a mask, thereby forming the through hole 216. The depth of the through hole 216 in this step is larger than that of the through hole 216 shown in FIG. 1. Further, notches F may be formed at the end of the through hole 216 as shown in FIG. 3. A case where the notches F are formed will be described below as an example.
Subsequently, in a step illustrated in FIG. 4, the protective tape 221 and the resist film 222 shown in FIG. 3 are removed and a back-grinding tape 224 is then attached to the upper surface 211A of the silicon substrate 211.
Then, in a step illustrated in FIG. 5, the silicon substrate 211 is ground from the lower surface 211B of the silicon substrate 211 and the silicon substrate 211 is then polished from the lower surface 211B of the silicon substrate 211, so that the notches F formed at the lower end of the through hole 216 are removed. If the thickness of the silicon substrate 211 is 250 μm before the grinding, the thickness of the silicon substrate 211 may be, for example, 200 μm after the grinding. Meanwhile, a polishing solution (slurry) containing abrasive grains is used to polish the silicon substrate 211.
Subsequently, in a step illustrated in FIG. 6, a back-grinding tape 224 shown in FIG. 5 is removed, and an insulating film 212 is formed on the both surfaces 211A and 211B of the silicon substrate 211 and the surface of the portion of the silicon substrate 211 corresponding to the side surface of the through hole 216. For example, an oxide film may be used as the insulating film 212.
In a step illustrated in FIG. 7, the through electrode 213 is formed by a known method in the through hole 216 on which the insulating film 212 is formed, and the wiring 214 is then formed. As a result, the substrate 200 is thus manufactured (see e.g., Japanese Patent No. 3816484).
FIGS. 8 to 10 are views to describe problems of the method of manufacturing the substrate in the related art. In FIGS. 8 to 10, the same components as those of the above-mentioned structure shown in FIGS. 2 to 7 are represented by the same reference numerals.
However, when the through hole 216 is formed by the Bosch process, acicular protrusions 227 made of silicon are formed on the portion of the silicon substrate 211 corresponding to the side surface of the through hole 216 as shown in FIG. 8.
Further, when the silicon substrate 211 is polished, abrasive grains 228 contained in the polishing solution (slurry) or polishing chips 229 adhere to the portion of the silicon substrate 211 corresponding to the side surface of the through hole 216 as shown in FIG. 9.
When the insulating film 212 is formed on the silicon substrate 211 that includes the acicular protrusions 227 and/or the abrasive grains 228 and the polishing chips 229 and then the through electrode 213 is formed, as shown in FIG. 10, there is a problem in that the insulating film 212 is not formed on the portion of the silicon substrate 211 corresponding to the side surface of the through hole 216 if the acicular protrusions 227 are broken, or the insulating film 212 is not formed on the side surface of the through hole 216 where the abrasive grains 228 or the polishing chips 229 adhere. If the above-mentioned problem occurs, there has been a problem in that it is not possible to sufficiently ensure an insulating property between the silicon substrate 211 and the through electrode 213 by the insulating film 212 formed on the through hole 216.